Process for photochemical production of aluminum printing forms



Patented Feb. 14, 1933 UNITED STATES PATENT OFFICE MAX THIMANN, OFBERLIN-WILMERSDORF, GERMANY, ASSIGNOR TO THE FIRM DR. IBEKK & KAULENCHEMISCHE FABRIK G. 11.3. 11., OF BERLIN-LICHTERFELDE, GER- MANY'PROCESS FOR PEOTOCHEMICAL PRODUCTION OF ALUMINUM PRINTING FORMS v NoDrawing. Application filed March 12, 1931, Serial No. 522,186, and inGermany March 17; 1930.

While it is easy in the photochemical production of zinc printing formsto remove the colloid coating fromthe exposed parts of the plate afterhaving exposed,'developed and etched the cleared parts of the platebefore such removal is being made, for example by means of alkali, thisremoval of the hardened colloid coating makes difiiculties when aluminumprinting forms are used.

Alkali cannot here be used for the removal before applying thesensitized colloid coat-- ing to the plate. Especially suitable for thispurpose are the sulphates of aluminum,

' chrome, iron and the like, and in first line the alums, such aspotassic aluminum alum,

iron ammonium alum, chrome potassium alum and so on.

By first treating the aluminum plate or similar aluminum printing formwith such a salt solution it is possible, easily to remove or wash oilthe parts of the coating hardened by exposure from the plate or thelike, which after said treatment with the salt solution has been coveredwith the sensitized colloid coating, exposed, developed and etched. Thisremoving of the hardened coating can be easily and quickly done withsuitable acids, especially phosphoric acid. Thereby as a rule it is notdissolving of the hardened coating which takes place, but

loosening of it from the metal plate or the like, so that the coatingcan be rinsed off the plate, either as a whole or in large pieces.

To attain the said effect it is, ior example, sufiicient to pour adiluted, say 1% solution of alum salt on to the clear metal plate, toleave it standing therewith for a short time,

then to'pour' ofi the said solution and to water the plate or the likeand to coat in.

the usual way with a sensitized colloidcoating.

The further treatment, exposing, developing and, if desired, etching ofthe plate can be done in the usual way, wherein for etching theclear-laid parts of the aluminum plate or the like, preferablyphosphoric acid, mixed with concentrated ferric-chloride can be used. Byusing the said mixture of phosphoric acid and ferric-chloride, for thepreparation of which a ferric-{chloride solution of at least contentsshould be used, and which therefore has either the consistency of apaste or of a viscid fluidity, one attains, that the etching medium onlyacts on the clear-lying parts of the plate and does not go to theexposedparts of the plate through the hardened coating which may becovered with a varnish or,resi= n layer, if required.

To remove the coating from the etched plate, a diluted phosphoric acid,e. g. a watery 10% phosphoric acid may expediently be used, whereby theloosening of the sensitized colloid coating from the plate previouslytreated with alum or the like, in the way above stated, is easilyattained.

- If the plate, which has first been treated inthe said way with saltsolutions, then spread with the sensitized colloidcoating, exposed anddeveloped, is to be etched, the parts of the plate to be protected fromthe action of the etching medium must be covered in known way with asuitable coatin In the above stated case, for an especia y suitablecover-coating a mixture of tannable organic substances, such ascopying-glue, and

tanning means, such as chrome alum are to be considered. The platehereinis treated for instance in that way, that a fresh mixture of aboutequal parts of copying-glue and a solution containing 5% chrome alum isbrought on to the parts of the'developed plate to be protected. Here themixture stifiens after some time owing to tanning setting in. The

stifiening may be quickened by heating the plate. The thus formedcovercoating protects the parts of the plate below it from the action ofthe etching means, for example from the above indicated mixture ofphosphoric acid and iron chloride. The removal of the coatings on theplate after the etching by means of phosphoric acid can then be doneforthwith, the protective coating formed from tannable substances andtanning means being dissolved from the plate with the hardened gelatinecoating in so far as the protective coating is arranged on the gelatinecoating, but on the other hand also from those par of the plate wherethe protective coating is situated directly on the metal of the plate,it

is directly dissolved without further ado by the action of theprosphoric acid.

Having now particularly described and ascertained the nature of my saidinyention,

i I declare that what I claim is 1. A process for the photochemicalproduction of aluminum printing-forms, comprising treating the aluminumbody with an acid-free solution of a salt of a tri-valent metal, coatinga sensitized-colloid coating onto the plate, exposing, developing, and

etching the plate, and then removing the hardeiied colloid-coating.

2. which the salt for treating the aluminum body,'prior to applying thesensitized colloid-coating, consists of an acid-free solution of ,asulphate of a tri -valent metal.

3. A process according to claim 1, in which the salt for treating thealuminum body, loid-coating, consists-of an acid-free solution of analum.

1 4. process for the photochemical production of aluminumprinting-forms, comprising treating the aluminum body with an acid-freesolution of a salt of a tri-valent metal, coating a sensitized-colloidcoating onto the plate, exposing, developing, and etching the plate, andthen removing the process according to claim 1 inv before applying thesensitized col acid and highly concentrated ferric-chloride, andremoving the hardened colloidcoamg from the metal by dilute phosphoricacl 8. A process for the photochemical production of aluminumprinting-forms, comprising treating the aluminum body with an my hand.

1 -MAX THIMANN.

hardenedcolloid-coating by means of a dilute acid.

5. A process according to claim 4-, in ;which the hardenedcolloid-coating remover is a water solution of phosphoric acid.

6. process for the photochemical production of aluminum printingiorms,comprising treating the aluminum body with an r acid-free solution ofa-salt of a tri-valent metal, applying a sensitized colloid-coatingthereover, exposing and developing the plate, etching the clear-lyingparts of. the plate with phosphoric acid, and removing the hardenedcolloid-coating from the metal 7 with dilute phosphoric acid.

thereover.

process for the photochemical production of aluminum printing-forms,comprising treating the aluminum body with an I acid-free solution of asalt of a tri-valent meta-l, applying a sensitized colloid-coatingexposing and developing the plate, etching the clear-lying parts of theplate by means of a mixture of phosphoric acid-free solution of a saltof a tri-valent

